The present invention relates generally to elevator controls and, in particular, to a method and an apparatus for assigning hall calls to a group of elevators.
There is shown in the European patent document EP-B 0 032 213 (corresponding to the U.S. Pat. No. 4,355,705) and in the European patent document EP-AA 0 356 731 (corresponding to the U.S. Pat. No. 4,991,694), for example, elevator group controls in which the intermediate floor calls are immediately assigned. These controls calculate, using a mathematical formula, a value called the cost of servicing or the operating cost corresponding to the waiting time of the passengers. This calculation is mainly based on the waiting time of the passengers on the floors as well as in the cars during an intermediate stop and the traveling time of the passengers in the cars. The operating costs are determined for every elevator of the group and are compared with each other, where the entered call is assigned to that car which exhibits the lowest cost. In this manner, the average waiting time of all passengers is minimized. In this type of elevator control, the well defined operational objective of minimizing the average waiting time is taken as the basis for the calculation formula. For attaining a different operational objective, as for example the minimization of long waiting times, these types of controls are not suitable.
Elevator group controls of the type described above are often used with elevator installations for the control of DOWN-peak and/or UP-peak traffic, as described for example in the German patent document DE-A 18 03 648 or in the European patent document EP-B 0 091 554 (corresponding to the U.S. Pat. No. 4,492,288). Elevator controls of this type make it possible to empty a building in relatively short time in case of extreme collective traffic incidence in the direction of a main floor, for example, at the end of the workday in an office building. In this case, the peak traffic portion of the control can be activated by a switch clock or by a measuring device determining the traffic flow in direction of the main floor, wherein at the same time the servicing of calls in the UP-direction can be reduced or completely eliminated. The control algorithm or calculation formula is based upon minimizing the waiting time of the passengers as well as increasing the transport capacity of the elevator group.
Until the above discussed switch clock or measuring device determining the traffic flow becomes active, a considerable time interval can occur during which not only the interfloor traffic but also the DOWN-peak traffic has to be serviced. This case can occur, for example, at the start of the lunch hour, at the closing hour of the office or through a sudden increase in the traffic at the end of a conference at one or several intermediate floors. In this case, few passengers occupy cars for upward travel so that the many passengers who want to travel downward are subjected to intolerably long waiting times. Besides, the transport capacity of the elevator group is under utilized in such a case.